Diabetes affects millions of people worldwide and this number is only increasing making it a recognized global health problem. The chronic disease results in long-term health disorders mainly including cardiovascular diseases and blindness. Currently, there is still no cure for diabetes available. Together with a healthy lifestyle, maintaining a normal blood glucose concentration by making therapeutic interventions (i.e. insulin delivery) is crucial for the prevention of the associated complications. Hereto glucose monitoring technologies are being used. By carefully controlling the blood glucose concentration, the quality and length of life will clearly improve.
Nowadays, most diabetes patients rely on hand-held glucose meters that record glucose levels in blood drawn via finger pricking. Since this procedure is not pain free and does not allow easy monitoring during the patient's sleep, researchers are looking into ‘user-independent continuous glucose monitors’ that can be implanted or used transdermal, i.e. through the human skin. Transdermal monitors in contact with the skin are categorized as non-invasive, but suffer from slow penetration and as a result a time lag between the blood-glucose level and the measured glucose level penetrating the skin (e.g. skin blister). Moreover these types of sensors can generate false signals when interacting with other molecules present in the sampled fluid and they are prone to environmental factors like e.g. temperature.
On the other hand, fully implantable devices are categorized as more invasive, but hold great promise since they increase the comfort and ease of adaptability for the patient if they can operate for a long time. In addition, implanted monitors are less affected by environmental factors or influencing ‘glucose-like’ molecules which are not present in the body fluid (except mannose). There are already a few continuous-in-vivo glucose monitors commercially available, such as the devices offered by US-based companies Medtronic and Abbott. These sensors make use of subcutaneously implantable needle-type electrodes that measure glucose in the interstitial fluid using enzymatic reactions. The lifetimes of these needle-type implants is limited due to the instability of the enzymes used and have to be replaced after few days. Moreover, most needle-type implants still have a part of the read out internal (the needle) and part external (the electronics) and this bears the risk of causing infection and inflammation because of the openings through the dermis. Minimally invasive implants should be developed without external parts and with long implantation times.